The present invention relates to a process for forming scrubbed stretch denim fabric and particularly relates to a process for forming the fabric employing a simplified finishing technique which is less costly, amenable to higher fabric production rates and has a reduced potential for off-quality fabric.
Various types of dyeing and finishing procedures have been used in the past to form scrubbed stretch denim fabric. For example, in U.S. Pat. No. 4,342,565, of common assignee herewith, the disclosure of which is incorporated herein by reference, there is set forth a method for forming fabric of this type, i.e., a weave of cotton and polyester spun blend warp yarns and a fill yarn, preferably formed of stretch polyester, that has been preferably air-textured and entangled or produced by false twisting and heat setting or other known texturing techniques. As set forth in that patent, the scrubbed stretch denim fabric typically includes 388 warp ends woven with the stretch fill yarns in a 2/1 RH twill pattern producing a greige construction width of about 66xc2xd inches with about 59 ends and 35 picks per inch and a finished construction width of about 58 inches with 68 ends and 39 picks per inch.
Over the years, that process has been modified to form essentially the same scrubbed stretch denim fabric construction. The process disclosed in U.S. Pat. No. 4,342,565, modified as currently employed to produce commercial scrubbed stretch denim fabric prior to the present invention is described with reference to FIG. 1 herein. The current methods have altered the patented process of U.S. Pat. No. 4,342,565 in many respects, including eliminating hot dyeing. The currently employed method of dyeing the yarns used to form present-day commercial scrubbed stretch denim fabric commences as illustrated in FIG. 1, with an initial scouring of the yarns using a scouring bath 10 similarly as set forth in U.S. Pat. No. 4,342,565 but with a different scouring solution. The current scouring bath is an aqueous solution comprised of 55 pounds of Sedgequest EDTA-100; 168 pounds of Caustic (50%); 52 pounds of Penetrant TER; and 3 pounds of a Defoamer 2403 and sufficient water to bring the total volume to 900 gallons. The yarns are passed through the dyeing process including the a scouring bath at a rate of about 38 yards per minute (YPM) and passed through the scouring bath 10 at a preferred scouring temperature of 190xc2x0 F. for 15 to 25 seconds. Following scouring, the yarns are rinsed in a series of baths 12 and 14 of hot water ranging in temperature from 160xc2x0 F. down to 80xc2x0 F, to remove natural oils, waxes or other additives from prior textile operations. The final rinsing is in a cold wash bath 16 at approximately 90xc2x0 F.
In contrast to the patented process set forth in U.S. Pat. No. 4,342,565, the current processing provides for dyeing wet on wet yarns. This is accomplished by increasing the squeeze roll pressure on the last wash bath prior to dyeing to maximize the wet pick-up potential. Thus, instead of passing the yarns over drying cans prior to dyeing as in the patented process, the yarns are introduced directly into the indigo dye bath. The dye bath is maintained at a temperature in a range of about 70xc2x0 to 90xc2x0 and preferably 85xc2x0 F. The currently employed indigo dye bath is preferably prepared in accordance with the following example wherein the indigo stock mix includes 171 pounds of caustic (50%), 23 pounds of dry hydrosulfite, 630 pounds of Indigo paste (20%), and 13 pounds of Penetrant TER and sufficient cold water to bring the total volume to 250 gallons. The hydro portion of the dye bath mix comprises 41 pounds of dry hydrosulfite and 44 pounds of caustic (50%) and sufficient cold water to bring the total volume of the hydro portion to 200 gallons. The hydro solution is mixed at a temperature of approximately 70xc2x0 F. and is mixed with the indigo stock mix, the combination of the indigo stock mix and hydro mix being maintained at an ambient temperature in a range of 70xc2x0-90xc2x0 F. and preferably approximately 85xc2x0 in the dye bath.
In the current method, the warp yarns make three passes through the dye baths indicated at 18, 20 and 22 in FIG. 1, with the warp yarn remaining immersed in each bath approximately 5 to 15 seconds and being skyed after each pass as discussed below. The immersion time of approximately 5 to 15 seconds is sufficient to have the dye solution penetrate the yarn. The reduced indigo, caustic and hydro mixture is continuously fed to the indigo dye baths to maintain a substantially constant indigo concentration level and to simultaneously maintain a high oxidation reduction potential of approximately 960 mv. In contrast to the patented process, the current process is to dye the yarns at normal temperatures. ranging from 70-90xc2x0 F. and preferably about 85xc2x0 F.
The yarns emerging from each dye bath are passed through the atmosphere or xe2x80x9cskyedxe2x80x9d for approximately one minute to complete reoxidizing the indigo. The skying following each dye bath 18, 20 and 22 is indicated at 19, 21 and 23, respectively, in FIG. 1. Subsequent to the final skying at 23, the warp yarn is washed in 3-7 successive running washes ranging in temperatures from 80xc2x0 F. to 140xc2x0 F. as indicated at 26, 28, 30, 32, 34 and 36 in FIG. 1. The preferred temperatures for the cold washes are indicated in FIG. 1. Subsequent to the cold washing of the dyed yarns, the yarns are passed through a softener mix maintained at a temperature of approximately 125xc2x0 F. The softener mix, as currently employed, comprises 190 pounds of Indilube C-20 in an aqueous mixture to obtain a total volume of approximately 400 gallons. The yarns are then dried over a series of dry cans 40, 42, 44, 46, 48, 50 and 52 as illustrated in FIG. 1. While the dyeing techniques currently used to dye yarns for forming commercial scrubbed stretch denim fabric are dissimilar in the foregoing respects from the dyeing technique disclosed in U.S. Pat. No. 4,342,565, the resulting textile product dyed by the current procedure has a similar indigo dye penetration deep into the fiber bundle without the yarns exhibiting the usual ring-dyed effect occurring in regular indigo dyeing.
Subsequent to dyeing the warp yarns, the dyed warp yarns and stretch fill yarns are woven to form the denim fabric and thereafter finished to produce the scrubbed appearance, proper hand and final finished stretch characteristics desired for the denim fabric. In the current finishing process as illustrated in FIG. 1, the woven fabric is first brushed and passed through a singer, as indicated at 54 and 56, respectively. Before passing the woven fabric through open width wash boxes as in the patented process, the current process passes the woven yarn through a preparation pad box wherein the fabric travels over a series of immersed rolls, and subsequently passed through a squeeze roll. This helps develop stretch by applying wet heat to reduce fabric width. A scouring agent is employed in the preparation pad box 58 to remove loose unfixed dye on the fabric. The preparation pad box includes a bath of 12 pounds Protowet 5917 and two pounds Defoamer 2403 in a water solution of approximately 875 gallons. Thus, the aqueous solution contains 0.17% of scouring agent.
As in the prior patented process, the woven fabric is then passed through a series of open width wash boxes schematically indicated at 60 for washing the fabric at temperatures in a range of 130-160xc2x0 F. These temperatures are lower than the corresponding processing temperatures set forth in the patented process. The wash boxes are maintained with a pH of about 10 or 11 and the fabric moves at approximately 65 yards per minute through the wash boxes. Subsequent to the wash boxes, the fabric is passed over a series of drying cans 62 with steam supplied the cans in a range of 30 to 60 pounds per square inch to provide a fabric moisture content of about 6-8%. Current industry standards indicate that to develop filling stretch, hot water and heat are necessary to reduce the width of the fabric and that the fabric should be tensioned in the warp direction. These standards are applicable to the current process.
Subsequent to drying, the fabric is finished by passing the fabric through a finishing pad 64. The finishing pad 64 comprises an aqueous solution of 160 pounds ITQ Softener HD 55, 16 pounds Sedgemul DNS-2, 5 pounds pigment, N Blue 2GC, 1 pound pigment Violet 4 BC, 33 pounds Discol 2007 and 1 pound Defoamer 2403 in sufficient water to bring the volume to 475 gallons. Maintained at 100-120xc2x0 F., the fabric is passed through the finish pad solution such that the solution is applied to the fabric with a 60% wet pick-up rate. Following application of the finish, the fabric passes onto a stack of drying cans 66 supplied with steam in a range of 0 to 30 psi to provide a fabric having a moisture content of about 18-20%. The fabric then enters a combined tenter frame and drying oven 68 which dries the fabric at a temperature in a range of approximately 180-220xc2x0 F. to provide a fabric with a moisture content of approximately 8-10%. The speed of the fabric passing through the finishing process from the scrubbing step 54 through the tenter and drying oven 68 is about 65 yards per minute. Rather than passing the fabric over a series of compressive shrinking machines to mechanically stretch the fabric, lessening the picks per inch in the greige fabric as in the patented process, the fabric is subjected to one compressive shrinking cycle in which the fabric is passed through the compressive shrinking machine at 48-52 yards per minute, achieving an 8-10% shrunk fabric width of 60-61 inches. From the compressive shrinking machine 70, the fabric is passed through a scrubbing operation, i.e., scrubber 72, at a speed of approximately 50 ypm, with surfaces in a range of 24-220 grit. As compared with the patented process, a second scrubbing operation was found to be unnecessary. Accordingly, the fabric following the scrubbing operation is passed through a final compressive shrinking machine 74 with the shrinking occurring in the warp direction at a rate of approximately 2% to about 8% to obtain a finished width of about 58.5-59.5 inches. The foregoing described current dyeing and finishing process produces a very similar scrubbed stretch denim fabric as in the process set forth in U.S. Pat. No. 4,342,565. However, the new process affords substantial advantages over both the patented and current processes described above.
As in the current process, the new process in accordance with the present invention does not employ hot dyeing as in U.S. Pat. No. 4,342,565. The resulting fabric is also somewhat similar employing a polyester and carded cotton blend for the warp yarns and a stretch polyester yarn for the fill yarns. In particular, an 8.50/1 blended cotton/polyester yarn comprised of 25% polyester (2xc2xc denierxc3x971xc2xd inches staple length) and 75% carded cotton is preferred. In the new process, the fabric typically includes 4008 warp ends woven with stretch fill yarns in a 2/1 RH twill pattern, producing a greige construction width of about 67xc2xd inches, with about 60 ends and 39 picks per inch in a finished construction width of about 60 inches with 68 ends and 39 picks per inch. The dyeing process for the new process according to the present invention is essentially the same as described above with respect to the current process. However, the finishing procedure is substantially different.
In accordance with the present invention, the dyed woven fabric is brushed and passed through a singer. Next, rather than passing the fabric through a series of open width wash boxes and maintaining the fabric under tension, the fabric is passed through a finishing pad with minimal tension and then passed through a series of pre-drying steam cans to afford a fabric moisture of 16-18%.
The new process thus eliminates the preparation pad, the open width washing and the pre-drying cycle prior to the finishing pad as in the current process. Yarn producers in the industry have consistently maintained that to develop filling stretch in fabrics, certain procedures should be followed in accordance with the yarn manufacturers"" specifications. Those manufacturers have stressed the importance of developing filling stretch by application of hot water and heat. Consequently, users of the yarns have typically provided the series of wash boxes and drying cans between the scouring and finish application steps as in the current process. However, in accordance with the present invention, it has been discovered that if the fabric is wetted out with normal finishing and is passed directly onto steam drying cans, the heat of drying produces steam on the fabric which develops filling stretch. Also, the tension normally applied to the fabric during finishing has been found to be detrimental. Thus, if the fabric is heated wet with very little tension, the fabric will tend to collapse on its own and, hence, develop filling stretch. Consequently, it is possible to finish the fabric in fewer and simplified steps at less expense and at faster production speeds with a higher potential of improved quality and reduced potential for off-quality goods. Employing the new process of the present invention also reduces the amount of pilling in the final fabric.
In a preferred embodiment according to the present invention, there is provided a process for finishing a stretchable woven denim fabric having cellulose containing warp yarns dyed with an indigo dye solution and stretch fill yarns, comprising the steps of (a) applying a finish including a pigment, a fixer, a surfactant and an anti-ozonate to the woven fabric, (b) subsequent to step (a), pre-drying the fabric, (c) setting the width of the fabric by disposing the fabric on a tenter frame, (d) subsequent to step (c), drying the fabric using steam cans, (e) subsequent to step (d), passing the fabric through a compressive shrinking machine and (f) scrubbing the fabric.